I can't offer much help unless you provide details about what you did. My guess is either a cacheing problem, or there is something contained in the data you are using to create the event that is causing the problem. Could you try with very simple test data so you can post it publicly if the problem is still there.
FWIW, common problems are having another facebook plugin active (obviously you need Otto's SFC installed and working - if it doesn't work, neither will SFCe). You also need your facebook account linked to your WP account, pop-ups not blocked in your browser, and be logged into facebook when you create the event.
If there is a bug I'd really like to fix it, so I'd be very grateful if we can get to the bottom of this.